Seems preemptive. There is already freedom of religion. If one is singled out and taxed unfairly then they can sue (and probably win).

That makes no sense. The government already decides what is and what is not a religion for tax purposes.

Sounds like the opposite. To qualify for religious tax exemption you need to actually prove to be, and practice as, a "real" religion. If there is no tax exception, it's more fair.

I can think of other ways to keep the government from taking sides in religions

As if governments were in the habit of arbitrarily handing out large scale tax exemptions. That idea might have been well-intended, but it's really a solution in search of a problem. And how would a religion be "taxed out of existence" anyways? Or the religion the belief or is the religion the org?